Method of manufacturing connector structures of integrated circuits

ABSTRACT

A die includes a substrate, a metal pad over the substrate, and a passivation layer covering edge portions of the metal pad. A metal pillar is formed over the metal pad. A portion of the metal pillar overlaps a portion of the metal pad. A center of the metal pillar is misaligned with a center of the metal pad.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/790,647, entitled “Connector Structures of Integrated Circuits,”filed Jul. 2, 2015, which application is a continuation of U.S. patentapplication Ser. No. 14/260,267, entitled “Connector Structures ofIntegrated Circuits,” filed Apr. 24, 2014, now U.S. Pat. No. 9,093,440,which application is a continuation of U.S. patent application Ser. No.13/276,090, entitled “Connector Structures of Integrated Circuits,”filed on Oct. 18, 2011, now U.S. Pat. No. 8,729,699, which applicationsare incorporated herein by reference.

BACKGROUND

Integrated circuits are made up of literally millions of active devicessuch as transistors and capacitors. These devices are initially isolatedfrom each other, and are later interconnected to form functionalcircuits. Typical interconnect structures include lateralinterconnections, such as metal lines (wirings), and verticalinterconnections, such as vias and contacts. Interconnect structures areincreasingly determining the limits of performance and the density ofmodern integrated circuits.

On top of the interconnect structures, connector structures are formed,which may include bond pads or metal bumps formed and exposed on thesurface of the respective chip. Electrical connections are made throughthe bond pads/metal bumps to connect the chip to a package substrate oranother die. The electrical connections may be made through wire bondingor flip-chip bonding.

One type of the connector structures includes an aluminum padelectrically connected to the interconnect structures formed of copper.A passivation layer and a polymer layer are formed, with portions of thepassivation layer and the polymer layer covering edge portions of thealuminum pad. An under-bump metallurgy (UBM) is formed to extend intothe opening in the passivation layer and the polymer layer. A copperpillar and a solder cap may be formed on the UBM and reflowed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a top view of a die, wherein connector structures aredistributed in corner regions, edge regions, and an inner region of thedie;

FIG. 2 illustrates a cross-sectional view of a portion of the die shownin FIG. 1;

FIGS. 3 and 4 illustrate the bonding of the die in FIG. 1 to anotherpackage component;

FIG. 5 schematically illustrates the misalignment of metal pillars fromrespective connecting underlying metal pads in accordance withembodiments, wherein the metal pillars and metal pads have non-elongatedshapes; and

FIG. 6 schematically illustrates the misalignment of metal pillars fromrespective underlying connecting metal pads in accordance withalternative embodiments, wherein the metal pillars and metal pads haveelongated shapes.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

Connector structures in semiconductor dies are presented in accordancewith an embodiment. The variations of the embodiment are then discussed.Throughout the various views and illustrative embodiments, likereference numbers are used to designate like elements.

FIG. 1 illustrates a top view of die 100 in accordance with variousembodiments. Die 100 may be a device die. Die 100 has corners 100A(including corners 100A1 through 100A4) and edges 100B (including edges100B1 through 100B4). A plurality of electrical connectors 50 may beformed at the surface of die 100. Electrical connectors 50 may beconnected to the underlying metal pads 40.

The details of exemplary electrical connectors 50 and metal pads 40 areshown in FIG. 2, which shows a cross-sectional view of a portion of die100, wherein the cross-sectional view is obtained from the planecrossing line 2-2 in FIG. 1. Die 100 includes semiconductor substrate30. In an embodiment, die 100 is a device die, which may includeintegrated circuits 32 having active devices such as transistors (notshown) therein. Semiconductor substrate 30 may be a bulk siliconsubstrate or a silicon-on-insulator substrate. Other semiconductormaterials including group III, group IV, and group V elements may alsobe used. In alternative embodiments, die 100 may be the die of otherpackage components that do not include active devices therein, and maybe an interposer die, for example. In the embodiments wherein die 100does not include active devices, die 100 may include passive devicessuch as resistors and capacitors, or free from passive devices.

Die 100 may further include inter-layer dielectric (ILD) 34 oversemiconductor substrate 30, and metal layers 36 over ILD 34. Metallayers 36 may include metal lines and vias (not shown) formed indielectric layers 38. In an embodiment, dielectric layers 38 are formedof low-k dielectric materials. The dielectric constants (k values) ofthe low-k dielectric materials may be less than about 2.8, or less thanabout 2.5, for example. The metal lines and vias may be formed of copperor copper alloys, although they can also be formed of other metals.

Metal pad 40 is formed over metal layers 36, and may be electricallycoupled to circuits 32 through the metal lines and vias in metal layers36. Metal pad 40 may be an aluminum pad or an aluminum-copper pad, andhence is alternatively referred to as aluminum pad 40 hereinafter,although other metallic materials may be used to form metal pad 40.Passivation layer 42 is formed to cover the edge portions of aluminumpad 40. The central portion of aluminum pad 40 is exposed through theopening in passivation layer 42. Passivation layer 42 may be a singlelayer or a composite layer, and may be formed of a non-porous material.In an embodiment, passivation layer 42 is a composite layer comprising asilicon oxide layer (not shown), and a silicon nitride layer (not shown)over the silicon oxide layer. Passivation layer 42 may also be formed ofun-doped silicate glass (USG), silicon oxynitride, and/or the like.Although one passivation layer 42 is shown, there may be more than onepassivation layer.

Polymer layer 46 is formed over passivation layer 42. Polymer layer 46may comprise a polymer such as an epoxy, polyimide, benzocyclobutene(BCB), polybenzoxazole (PBO), and the like. Polymer layer 46 ispatterned to form an opening, through which aluminum pad 40 is exposed.The patterning of polymer layer 46 may be performed using photolithography techniques.

Under-bump metallurgy (UBM) 48 is formed over metal pad 40. UBM 48comprises a first portion over polymer layer 46, and a second portionextending into the opening in polymer layer 46. In an embodiment, UBM 48includes a titanium layer and a seed layer, which may be formed ofcopper or copper alloys. Metal pillar 50 is formed on UBM 48, and isco-terminus with UBM 48. The edges of UBM 48 are aligned to respectiveedges of metal pillar 50. UBM 48 may be in physical contact with metalpad 40 and metal pillar 50. In an exemplary embodiment, metal pillar 50is formed of a non-reflowable metal(s) that does not melt in reflowprocesses. For example, metal pillar 50 may be formed of copper or acopper alloy. The top surface 50B of metal pillar 50 is higher than topsurface 46A of polymer layer 46. In addition to metal pillar 50, theremay be additional metal layers such as metal layer 52 formed on metalpillar 50, wherein metal layer 52 may include a nickel layer, apalladium layer, a gold layer, or multi-layers thereof. Solder cap 54may also be formed on metal layer 52, wherein solder cap 54 may beformed of a Sn—Ag alloy, a Sn—Cu alloy, a Sn—Ag—Cu alloy, or the like,and may be lead-free or lead-containing. UBM 48 may also be consideredas the bottom part of the metal pillar 50.

In an embodiment, lateral dimension W1 of metal pad 40 is smaller thanlateral dimension W2 of metal pillar 50. In alternative embodiments,lateral dimension W1 of metal pad 40 is equal to or greater than lateraldimension W2 of metal pillar 50.

Metal pad 40 as shown in FIG. 2 is misaligned with the respectiveoverlying metal pillar 50. In the top view of the structure in FIG. 2,metal pad 40 has center 40A (also refer to FIGS. 5 and 6), which isshown as line 40A in FIG. 2. Metal pillar 50 also has center 50A in thetop view, which is shown as line 50A in FIG. 2. In accordance withembodiments, center 40A is misaligned with center 50A by distance ΔS. Inexemplary embodiments, misalignment ΔS may be smaller than about 0.2percent, or between about 0.01 percent and about 0.09 percent, of lengthL or width W (FIG. 1), wherein length L and W are the length and thewidth of die 100. Misalignment ΔS is measured in the same directionlength L or width W is measured, depending on the direction of thealignment.

In FIG. 2, arrow 45 is drawn to illustrate the direction of center 100C(also refer to FIG. 1) of die 100. Accordingly, depending on thelocation of metal pad 40 and metal pillar 50 in die 100, the directionopposite to direction 45 may be toward corners 100A1-100A4 or edges100B1-100B4 of die 100. As shown in FIG. 2, in the direction toward diecenter 100C, the overlapping region of metal pillar 50 and polymer layer46 has width W3, and in the direction away from die center 100C, theoverlapping region of metal pillar 50 and polymer layer 46 has width W4,which is greater than width W3. As a result of the misalignment of metalpillar 50 and metal pad 40, metal pillar 50 overlaps more with polymerlayer 46 in the direction away from die center 100C than with polymerlayer 46 in the direction toward die center 100C. This helps reduce thecracking in dielectric layer 42.

Referring to FIG. 3, die 100 is bonded to package component 200, whichmay be a package substrate, a print circuit board (PCB), or aninterposer, for example. Accordingly, package component 200 is referredto as package substrate 200, although it may also be another type ofpackage components such as an interposer, a device die, a PCB, or thelike. In an embodiment, package substrate 200 includes metal pad 210,and dielectric layer 212 covering portions of metal pad 210. Metal pad210 may be exposed through an opening in dielectric layer 212, and metalpillar 50 may be bonded to metal pad 210 through the opening. In anembodiment, after the bonding, center 210A of metal pad 210 may bealigned with center 50A of metal pillar 50, and misaligned with center40A of metal pad 40. Alternatively stating, metal pad 210 may be alignedwith metal pillar 50, and misaligned with metal pad 40. It is realizedthat package substrate 200 may have a first coefficient of thermalexpansion (CTE) different from, and possibly greater than, a second CTEof die 100. Accordingly, center 210A of metal pad 210 may need to bemisaligned with center 50A of metal pillar 50 before the reflow process,so that when heated in the reflow, due to the difference between thefirst and the second CTEs, center 210A of metal pad 210 is aligned withcenter 50A of metal pillar 50. After cooled down from the reflow, center210A of metal pad 210 may stay aligned with center 50A of metal pillar50. Accordingly, in the design of metal pad 40, metal pillar 50, metalpad 210, and the respective die 100 and package component 200, theexpansion of the materials need to be taken into account.

FIG. 4 illustrates a connector structure in accordance with alternativeembodiments. In addition to the misalignment between center 40A of metalpad 40 and center 50A of metal pillar 50, center 210A of metal pad 210is also misaligned with center 50A of metal pillar 50. In the formationof the respective package, center 210A of metal pad 210 may be alignedwith center 50A before the reflow. After the reflow, due to thedifference between the CTEs of die 100 and package substrate 200, themisalignment between metal pad 210 and metal pillar 50 may occur.

Referring back to FIG. 1, die 100 includes inner region 64C encircled bya peripheral region. The peripheral region may be divided into cornerregions 64A (including 64A1 through 64A4), which are adjacent to corners100A of die 100, and edge regions 64B (including 64B1 through 64B4),which are adjacent edges to 100B of die 100. Length L5 and width W5 ofedge regions 64B and corner regions 64A may be smaller than one fourth,or smaller than about 10 percent, of the respective length L and width Wof die 100. In each of corner regions 64A, edge regions 64B, and innerregion 64C, there may be a plurality of connector structures, eachincluding metal pad 40 and an overlying metal pillar 50, as also shownin FIG. 2.

FIG. 5 schematically illustrates how metal pillars 50 may be misalignedwith respective underlying metal pads 40, wherein the misalignment ofcenters 40A and 50A represent the misalignment of the respective metalpad 40 and metal pillar 50. In each of corner regions 64A, edge regions64B, and inner region 64C, one metal pad 40 and one metal pillar 50 isillustrated to represent the plurality of metal pads 40 and metalpillars 50 in the same region. As shown in FIG. 5, centers 50A in edgeregions 64B are shifted toward the respective edges 100B relative tocenters 40A of the respective connecting metal pads 40. For example,centers 50A in edge regions 64B1 are shifted toward edge 100B1, whilecenters 50A in edge regions 64B3 are shifted toward edge 100B3. Theshifting directions (as indicated by dashed arrows 102) are away fromcenter 100C of die 100.

As indicated by the misalignments between centers 40A and 50A, metalpillars 50 in corner regions 64A are shifted toward the respectivecorners 100A relative to the respective connecting metal pads 40. Forexample, centers 50A in corner region 64A1 are shifted toward corner100A1, while metal pillars 50 in corner regions 64A3 are shifted towardcorner 100A3. The shifting directions (as illustrated by dashed lines102) in corner regions 64A are further away from center 100C. For metalpads 50 in corner regions 64A, the shifting directions may be parallelto the lines drawn between center 100C and corners 100A. For metal pads50 in edge regions 64B, the shifting directions are perpendicular to theextending direction of the respective edges 100B. In each of cornerregions 64A, there may be one, two, three, or more corner rows ofconnector structures having shifted centers 40A/50A, while the rest ofmetal pads 40 and the respective metal pillars 50 in the corner regions64 have their centers aligned. In each of edge regions 64B, there may beone, two, three, or more edge rows of connector structures havingshifted centers 40A/50A, while the rest of metal pads 40 and therespective metal pillars 50 in the corner regions 64 have their centersaligned. Alternatively, in each of corner regions 64A and edge regions64B, all connector structures having their metal pads 40 misaligned withthe respective metal pillars 50. In inner region 64C, centers 40A ofmetal pads 40 are aligned with the centers 50A of the respectiveoverlying metal pillars 50. In some embodiments, no connector in innerregion 64C has misaligned centers 40A and 50A.

In FIG. 5, metal pads 40 and metal pillars 50 are substantially circularsymmetrical with no significantly longer and shorter axis (when viewedin the top view). In alternative embodiments, metal pads 40 and metalpillars 50 may have elongated shapes, with a long axis significantlygreater than a short axis. FIG. 6 illustrates a top view of an exemplarydie 100. This structure is similar to the structure shown in FIG. 5,except the top view shapes of metal pad 40 and metal pillar 50 arestretched in directions, for example, toward center 100C of die 100.This structure may be used for forming bump-on-trace structures. Theconnector structures in corner regions 64A and edge regions 64B maystill include connector structures whose metal pillars 50 are shiftedaway from center 100C of die 100 relative to the correspondingunderlying metal pads 40. On the other hand, in inner region 64C,centers 40A of metal pads 40 and the centers 50A of the overlying metalpillars 50 are still aligned.

In the embodiments, by shifting metal pillars away from the center ofthe respective die relative to the respective connecting metal pads, theconnector structures are more robust, and the likelihood of havingpassivation cracking is reduced. Experimental results indicated that thepassivation cracking, when happened, are more likely to occur on thesides of the metal pads away from the center of the die. On the sidestoward the center of the die, the passivation cracking is unlikely tooccur. Therefore, by shifting the metal pillars, in the directions awayfrom the center of the die, there is more overlap of metal pillars andpolymer layer 46 (FIG. 2). Accordingly, the passivation cracking isreduced.

In accordance with embodiments, a die includes a substrate, a metal padover the substrate, and a passivation layer covering edge portions ofthe metal pad. A metal pillar is formed over the metal pad. A portion ofthe metal pillar overlaps a portion of the metal pad. A center of themetal pillar is misaligned with a center of the metal pad.

In accordance with other embodiments, a die includes a substrate, afirst metal pad over the substrate, a passivation layer covering edgeportions of the first metal pad, and a first metal pillar over the firstmetal pad and extending over the passivation layer. The first metal padand the first metal pillar are in a first corner region of the die. Thedie further includes a second metal pad over the substrate, and a secondmetal pillar over the second metal pad. The second metal pad and thesecond metal pillar are in a second corner region of the die. The firstand the second corner regions are on opposite sides of a center of thedie. In a top view of the die, centers of the first and the second metalpillars are misaligned with centers of first and the second metal pads,respectively, and are shifted away from the center of the die relativeto the centers of first and the second metal pads, respectively.

In accordance with yet other embodiments, a die includes a first, asecond, a third, and a fourth corner. The die further includes asubstrate, a first, a second, a third, and a fourth metal pad over thesubstrate, wherein the first, the second, the third, and the fourthmetal pads are closer to respective ones of the first, the second, thethird, and the fourth corners than any other metal pad in the die. Thedie further includes a passivation layer covering edge portions of thefirst, the second, the third, and the fourth metal pads. A first, asecond, a third, and a fourth metal pillar are disposed over respectiveones of the first, the second, the third, and the fourth metal pads, andextending into openings in the passivation layer to electrically coupleto the first, the second, the third, and the fourth metal pads. Centersof the first, the second, the third, and the fourth metal pads areshifted away from centers of the first, the second, the third and thefourth metal pads in directions toward the first, the second, third, andthe fourth corners, respectively.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: providing a device diecomprising: a first metal pad; a passivation layer comprising a portionover the first metal pad, wherein the passivation layer has an opening,with the opening having a first center in a top view of the device die;an Under-Bump Metallurgy (UBM) extending into the passivation layer tocontact the first metal pad; and a non-solder metal pillar over andcontacting the UBM, wherein the non-solder metal pillar has a secondcenter in the top view of the device die, with the second centermisaligned with the first center; aligning a package substrate to thedevice die; and performing a reflow to bond the non-solder metal pillarto a second metal pad of the package substrate.
 2. The method of claim1, wherein before the reflow, a third center of the second metal pad inthe package substrate is misaligned with the second center.
 3. Themethod of claim 2, wherein during the reflow, the third center issubstantially vertically aligned to the second center.
 4. The method ofclaim 2, wherein after the reflow, the third center is substantiallyvertically aligned to the second center.
 5. The method of claim 1,wherein before the reflow, a third center of the second metal pad in thepackage substrate is vertically aligned to the second center.
 6. Themethod of claim 5, wherein after the reflow, the third center isvertically misaligned with the second center.
 7. The method of claim 6,wherein after the reflow, the third center is shifted farther away froma center of the device die than the second center.
 8. The method ofclaim 1, wherein the second center is shifted from the first center in adirection away from a center of the device die.
 9. The method of claim8, wherein in the direction away from the center of the device die, theUBM extends beyond a respective edge of the first metal pad, and in adirection toward the center of the device die, the UBM is recessed froma respective edge of the first metal pad.
 10. A method comprising:forming a device die comprising: forming a passivation layer covering afirst metal pad; forming an opening in the passivation layer to expose acenter portion of the first metal pad, wherein a first center of thefirst metal pad is aligned to a second center of the opening; andforming an Under-Bump Metallurgy (UBM) extending into the opening,wherein the UBM has a third center misaligned with the first center andthe second center.
 11. The method of claim 10, wherein the third centeris shifted farther away from a center of the device die than the firstcenter.
 12. The method of claim 10 further comprising forming a metalpillar over the UBM.
 13. The method of claim 12, wherein the UBM has acenter aligned to the third center, and the UBM and the metal pillar areco-terminus.
 14. The method of claim 10 further comprising: aligning afourth center of a second metal pad of a package component to the thirdcenter; and bonding the package component to the device die.
 15. Themethod of claim 14, wherein after the bonding, the fourth center isshifted away from a center of the device die farther than the thirdcenter.
 16. The method of claim 10 further comprising: aligning apackage component to the device die, wherein a fourth center of a secondmetal pad of the package component is misaligned with the third center;and bonding the package component to the device die.
 17. The method ofclaim 16, wherein the bonding comprises reflowing a solder region incontact with the second metal pad, and after the reflowing the solderregion, the fourth center is aligned to the third center.
 18. A methodcomprising: forming a device die comprising: forming a passivation layercovering a metal pad; forming an opening in the passivation layer toexpose a center portion of the metal pad; and forming a metal pillarover and electrically coupled to the metal pad through the opening,wherein in a cross-sectional view of the metal pad and the metal pillar,the metal pillar has a first edge and a second edge opposite to eachother, wherein the first edge overlaps the metal pad, and the secondedge is vertically misaligned from the metal pad; and bonding the devicedie to a package component, wherein a solder region bonds the metalpillar to a metal pad of the package component.
 19. The method of claim18, wherein the first edge is closer to a center of the device die thanthe second edge.
 20. The method of claim 19, wherein a vertical planefrom which the cross-sectional view is obtained passes a center of themetal pad and a center of the metal pillar, and the vertical planefurther passes the center of the device die.